This invention relates to apparatus for measuring a three phase alternating current input voltage by converting the phase voltages into currents, adding the negative half-wave currents, reversing the polarity of the added current to provide a positive current and converting the positive current into a positive output voltage which is a measurement of the input voltage.
It is often necessary to measure a three phase alternating current input voltage to insure, for example, that the amplitude of the input voltage is within desired limits. The measurement can be achieved by using full or half-wave summing rectifier apparatus.
Full wave summing rectifier apparatus tends to be complex in construction.
Negative half-wave summing rectifier apparatus according to the invention has distinct advantages in that it features a minimum number of components, is powered by a single, positive power supply and permits the use of external resistors. The apparatus of the invention is thus simple in construction and is effective for the purpose described since the inputs to the apparatus are at zero volts for a small percentage of the time and there are no errors during the positive half cycles of the input voltages, as will be discerned from the description of the invention which follows.